A disk-type recording medium such as a compact disk (CD) can store high-quality digital audio data permanently, so that it is very popular recording medium. Recently, a digital versatile disk (referred as ‘DVD’ hereinafter) has been developed as a new disk-type recording medium. A DVD can store much larger size than a CD, thus, high-quality moving picture or audio data are recorded on a DVD for much longer time. Therefore, a DVD will be used widely in the near future.
There are three types of a DVD, DVD-ROM for read-only, DVD-R for write-once, and DVD-RAM or DVD-R/W for rewritable. For a rewritable DVD, the standardization of data writing format is in progress.
In these days, various types of digital audio data are provided through a data network such as Internet. Such audio data are called EMD (Electronic Music Distribution) audio data. EMD audio data are provided by a lot of contents providers. However, the contents providers encode EMD audio data to mutually different formats and add different unique copy-protection codes to EMD audio data as well to prevent unauthorized copy and protect their copyright.
Therefore, a decoder and a decryption code adequate for downloaded EMD audio data must be obtained from a contents provider having provided the EMD audio data before playing the downloaded EMD audio data. The decryption code is used for decrypting EMD audio data encrypted with a corresponding copy-protection code.
Because it is nearly impossible to obtain both a suitable decryption code and a decoder without lawful approval, EMD audio data can be protected against unauthorized copy, thus its copyright can be protected well.
As mentioned before, because a large-capacity recording medium is being commercialized and anti-piracy of EMD audio data becomes possible, it is expected that EMD audio data are spread greatly over a data network in the near future.
However, EMD audio data, in general, are entirely encrypted with a copy-protection code. Therefore, a user can not play any piece of EMD audio data downloaded onto a writable DVD through a disk device before he or she purchases a decryption code. In other words, a user can not confirm at all whether the downloaded EMD audio data are what he or she wants or whether its audio quality is better or not than he or she expected.
Consequently, a user hesitates to buy a play-authorizing code, namely, a decryption code for the downloaded EMD audio data, which would impede spread and distribution of digital audio data through a data network such as Internet.